Mini-computer systems and main-frame computer systems typically employ disk drives for mass information storage. Generally, such systems are not portable and are housed in large rooms having controlled environments. Consequently, the weight and space occupied by such systems are of little concern. Recently, however, the advent of personal computer systems and portable computer systems has placed a premium on providing disk drives of reduced size and weight. Exemplary of such a disk drive is U.S. Pat. No. 4,712,416 which issued on Dec. 8, 1987, to Moon et al. for a "Thin and Compact Micro-Winchester Head and Disk Assembly". The invention of Moon et al., includes a housing for containing a 95 mm hard disk that provides at least ten megabytes of storage, a spindle motor for rotating the hard disk and a rotary actuator assembly for moving transducers relative to the hard disk. The disk drive is 63/4" in length, 4" in width and has a height of 1" exclusive of a printed circuit board. Also known is the disk drive disclosed in International Application WO 88/09551, which published on Dec. 1, 1988, and is entitled "Disk Drive Architecture". Disclosed is a disk drive apparatus that includes a base-plate that provides a mounting surface for a spindle motor that rotates a 3.5" hard disk and a rotary actuator assembly that moves transducers relative to the hard disk. The base-plate is attached to an end-plate. The base-plate/end-plate assembly fits into, and establishes a seal with, an open-ended casing. A unitized frame attaches the end-plate/casing assembly to a printed circuit board and provides shock absorbing capability. The disk drive is 53/4" in length, 4" in width and has a height of 11/2". Conner Peripherals also produces a low-profile disk drive which is approximately 53/4".times.4".times.1". Also known is the Model 220 disk drive produced by the assignee of the present invention and the subject of U.S. patent application Ser. No. 07/162,799 and International Application WO 89/08313, which are incorporated herein by reference. The Model 220 disk drive includes a housing for containing two hard disks with each providing an information storage capacity of 5-10 MBytes, a spin motor for rotating the hard disks, transducers for communicating with the hard disk, and a rotary actuator for moving the transducers relative to the hard disks. A printed circuit board having circuitry for controlling various components of the disk drive and the housing are attached to one another in a stacked relationship that results in an overall length of 4.30", a width of 2.80" and a height of 1.00" for the disk drive including the printed circuit board.
Of importance in achieving a reduced height dimension is the height of the components contained within the disk drive housing and especially the height of the spin or spindle motor that rotates the hard disk(s). Presently, spin motors have heights on the order of 0.6 inches. Exemplary of such a spin motor is the aforementioned Model 220 disk drive produced by the assignee of the present invention.
Also of importance in attaining a low profile disk drive is the height profile of the rotary actuator. The rotary actuator disclosed in the aforementioned patent to Moon et al., includes a triangular electromagnetic voice coil surrounded by upper and lower magnets. Surrounding the upper and lower magnets are flux return plates that are attached to the housing and constrain the magnetic fields produced by the magnets to a gap area between the magnets as well as prevent the magnetic fields produced by the magnets and the voice coil from affecting the hard disk(s). Consequently, the height of at least a portion of the rotary actuator is defined by two flux return plates, two sets of magnets and a voice coil. The Model 220 disk drive uses a similar arrangement. The rotary actuator used in the disk drive disclosed in International Application WO 88/09551 includes an electromagnetic voice coil that surrounds a center pole. The center pole cooperates with a base plate and a top plate located below and above, respectively, of the electromagnetic voice coil to provide flux return paths. Consequently, the height of the rotary actuator is determined by the voice coil, the center pole and the top and bottom plates. Also known are linear voice coil actuators that have a housing that provides a surface for attaching the actuator to the disk drive housing. The actuator housing provides a flux return path as well as prevents the entry of contaminants into the disk drive housing.
Of related interest in producing a disk drive of reduced height is the attachment to the housing of a printed circuit board having electronics for controlling one or more of the components of the disk drive. The U.S. Pat. No. 4,712,416 to Moon et al., discloses a printed circuit board having electronics for controlling the multiple windings of the spindle motor. To attain a low profile disk drive, the printed circuit board is located in a recess located on the exterior of the baseplate and adjacent the spindle motor. Apparently, the circuitry for controlling other aspects of the disk drive, like read/write control and actuator servo control, are located on another printed circuit board. The International Application WO 88/09551 illustrates a printed circuit board that is attached to the casing by a frame and provides electronics for controlling the hardware housed within the casing. The portion of the casing facing the printed circuit board appears to be devoid of any recesses. Consequently, the printed circuit board must be spaced from the casing by a distance greater than the highest profile component on the side of the printed circuit board facing the casing. The Model 220 disk drive piggybacks the disk drive housing on the printed circuit board. The portion of the housing facing the printed circuit board includes a first level defined by the spin motor and the rotary actuator, a second level recessed from the first level and a third level recessed from the second level. Electronic components are located on the side of the circuit board facing the housing to take advantage of the recesses defined by the second level. A connector for establishing a communication link between the electronics on the circuit board and a flexible circuit that extends into the housing and communicates with components contained therein is located on the side of the circuit board facing the housing and utilizes the recess defined by the third level.
Another important aspect associated with disk drives employed in personal and/or portable computer systems is the frame used to attach the housing and/or printed circuit board to the user's computer system. The Model 220 disk drive does not use a frame. Instead, the Model 220 uses the printed circuit board to bottom mount the disk drive to the user's computer system as well as support the housing. The light weight of the housing and the components contained therein makes such an arrangement possible. While such a configuration reduces cost, saves space and reduces the overall size of the disk drive, it lacks shock absorbing capability, has grounding problems and does not accommodate other mounting configurations. The frame of the disk drive disclosed in International Application WO 88/09551 supports both the printed circuit board and the housing. The frame also provides side and bottom mounting capability together with shock absorbing capability. However, the frame has a surface area that requires grounding and does not provide top mounting capability. The disk drive produced by Conner Peripherals employs a housing having a base-plate with two side rails that provide side and bottom mounting capability.
An important factor affecting the performances of disk drives is the entry of contaminates, such as dirt or dust or moisture, into the housing. Presently, disk drives use ambient or breather filters to prevent the entry of contaminants, like dust and dirt, into the interior of the housing. Exemplary of such filters are the ones employed in the Model 220 disk drive and the disk drive disclosed in the patent to Moon et al. While ambient or breather filters inhibit the entry of dust and dirt into the interior of the disk drive housing, they are ineffective at inhibiting the entry of water vapor. Consequently, desiccants contained within box-like structures have been placed in the interior of the housing to adsorb water vapor contained therein. The Model 220 disk drive uses a desiccant contained within a box-like structure. While a relatively large amount of desiccant can be provided in this way, the use of box-like structures creates longer diffusion paths, i.e. the distance a water molecule must travel upon entering box-like structures before adsorption occurs. The longer adsorption paths, in turn, reduce the rate of adsorption of the desiccant.
Also of importance to the operation of a disk drive is the effect that the flexible circuit used to communicate with a rotary actuator and/or transducers attached to the rotary actuator has on the rotary actuator. Typically, flexible circuits exert a force or torque on the rotary actuator. This torque affects the position of the transducers or heads relative to the disk. The disk drive apparatus disclosed in the International Application WO 88/09551 reduces this effect of the flexible circuit on the rotary actuator by using a flexible circuit with as large a radius of curvature as possible. The Model 220 disk drive imposes a double-curve on the flexible circuit to reduce its effect on the rotary actuator.